Other then the pumping lemma, you could also use closure properties to prove that a language isn't context free (the family of context free languages is closed under union, concatenation, the star operation, homomorphism, inverse homomorphism and intersection with regular languages, but it's not closed under intersection and complement).
What you need to do from here is to assume that the language at hand is context free, use a combination of the operations above to get a language which is not context free, which yields a contradiction and thus, you'll achieve what you were trying to prove.
Good luck!